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1.
About seven hundred gravity stations were established 2–3 miles apart over the Precambrian terrain of Singhbhum that lies between latitude 22° 15′ to 23°°15′N and longitude 85° to 87°E. Bouguer anomalies ranging from +4 to −62 mGal are found in the area. The observed Bouguer anomaly map was analyzed into regional and residual components. The residual anomaly map shows an excellent correlation with geology. The Singhbhum granite batholith is associated with several gravity lows. The residual anomaly map outlines nine plutonic granitic masses within the Singhbhum batholith. Negative residuals are also observed over some intrusive granites outside the batholith. Residual gravity highs are noted over the Dalma hill as well as over the Dhanjori lava complex on the eastern part of the Singhbhum batholith.Two-dimensional models suggestive of subsurface configuration of several major geologic units in the area are presented. These indicate that some of the plutonic granites within the Singhbhum batholith are of relatively large dimensions. The basin containing the Iron Ore Group of rocks to the west of the batholith, as well as the basin containing Singhbhum Group of rocks outside the Copper Belt thrust, may have sedimentary thicknesses of the order of 6–7 km. The Dalma lavas attain their maximum thickness of about 2.5 km in the form of a syncline, underneath which the Singhbhum Group of rocks is also found to be the thickest. The Copper Belt thrust, a major Precambrian fracture around the Singhbhum batholith, is moderately north-dipping near the surface but possibly attains a steeper slope at depth. The thrust appears to be quite deep seated. A threedimensional computer-based model for the Dhanjori lava—gabbro complex on the eastern part of the Singhbhum batholith has been deduced. Maximum thickness of these basic rocks is found to exist underneath a thin cap of granophyre. The geological implication of these results is discussed.Variation in the regional anomalies seems to be attributable to a mass deficiency under the Singhbhum batholith. The batholith may extend subsurfacially towards the north across the Copper Belt thrust. The northern tip of the batholith probably became dissected along the line of intersection of the two orogenic trends in the area and subsided. Over this subsided part, the Singhbhum Group of rocks was deposited at a later stage. Gravity data suggest a fairly large amount of subsidence in the area. 相似文献
2.
ANISOTROPIC FEATURE OF QIANGTANG MASSIF TEXTURE 总被引：2，自引：1，他引：1
ANISOTROPIC FEATURE OF QIANGTANG MASSIF TEXTURE 相似文献
3.
Study on the Gravity Field and Deep-Seated Crustal Structure at the North Margin of the Qinghai-Tibet Plateau 总被引：1，自引：0，他引：1
MENG Lingshun 《Continental Dynamics》1997,(1)
1.I~ductionThenorthernmarginoftheQinghai-TibetplateauincludestheAltllnMis.,theQilianMis.,KunlunMis.,theQaidambasinandthesouthernTarimbasin.ThisareaistCctonicallycharacterizedbyintensiveCenozoicdeformationwithcomplicateddeformationalmechedsm(Molnaretal.,1987;Zheng,1991;Culetal.,1994;Ding,1995andXuetal.,1996).Thedeformationalmechanismsincludethrust-napping,strike-slipping,extensionandblockrotation,aswellassimultaneousupliftingandtypicalbasin-rangetectonics(CulandXu,1996).IntermsofCenozoi… 相似文献
4.
The most recent seismic profiles in southern Italy show the existence of a sudden thinning of the crust at the boundary between the chain and the Tyrrhenian margin. The abrupt change in thickness can be followed along a zone which has the same geometry in plan as the Calabrian arc. By considering these data and the gravimetric anomalies, it is possible to associate this crustal anomaly with a deep-seated shear zone which determines a crustal shortening of about 40–60 km which can only be a consequence of post-Tortonian tectonics. The surface equivalents of the deep-seated shear zone can be recognized, from north to south, in the alignment of the intra-Apenninic basins (Vallo di Diano, San Arcangelo, Potenza), in the Crati-Mesima graben and in the Mount Kumeta-Alcantara fault zone.The distribution of the seismicity and its connection with the surface structures shows that the largest earthquakes occur along the deep shear-zone. In particular, shocks with the highest magnitude and the longest recurrence intervals are located in those areas where the deep shear zone is at an angle of about 90° with the direction of maximum shortening (Crati-Mesima graben). The fault zones nearly parallel to the regional compression axis (e.g., Mount Kumeta-Alcantara fault zone) are characterized by earthquakes of lower magnitude. Taking into account the neotectonic evolution of the regional structures, as well as the orientation of the stress field and its connection with the deep-seated shear zone, it is possible to distinguish the following seismotectonic zones: Upper Crati-Mesima graben, transverse throughs, Mount Pollino-Mount Raparo fault zone, external Ionian area, San Arcangelo basin-zone of the external flysch, Sicani Mountains, Mount Kumeta-Alcantara fault zone, Caltanissetta basin, and Iblean plateau-Bradanic trough-Murge ridge. The definition of the geometry of the shear zone at depth is one of the most important, but still unresolved problems. 相似文献
5.
Tuhin Chakraborty Dewashish Upadhyay Sameer Ranjan Kamal L. Pruseth Jayanta K. Nanda 《Journal of Metamorphic Geology》2019,37(1):113-151
The Central Indian Tectonic Zone (CITZ) is a Proterozoic suture along which the Northern and Southern Indian Blocks are inferred to have amalgamated forming the Greater Indian Landmass. In this study, we use the metamorphic and geochronological evolution of the Gangpur Schist Belt (GSB) and neighbouring crustal units to constrain crustal accretion processes associated with the amalgamation of the Northern and Southern Indian Blocks. The GSB sandwiched between the Bonai Granite pluton of the Singhbhum craton and granite gneisses of the Chhotanagpur Gneiss Complex (CGC) links the CITZ and the North Singhbhum Mobile Belt. New zircon age data constrain the emplacement of the Bonai Granite at 3,370 ± 10 Ma, while the magmatic protoliths of the Chhotanagpur gneisses were emplaced at c. 1.65 Ga. The sediments in the southern part of the Gangpur basin were derived from the Singhbhum craton, whereas those in the northern part were derived dominantly from the CGC. Sedimentation is estimated to have taken place between c. 1.65 and c. 1.45 Ga. The Upper Bonai/Darjing Group rocks of the basin underwent major metamorphic episodes at c. 1.56 and c. 1.45 Ga, while the Gangpur Group of rocks were metamorphosed at c. 1.45 and c. 0.97 Ga. Based on thermobarometric studies and zircon–monazite geochronology, we infer that the geological history of the GSB is similar to that of the North Singhbhum Mobile Belt with the Upper Bonai/Darjing and the Gangpur Groups being the westward extensions of the southern and northern domains of the North Singhbhum Mobile Belt respectively. We propose a three‐stage model of crustal accretion across the Singhbhum craton—GSB/North Singhbhum Mobile Belt—CGC contact. The magmatic protoliths of the Chhotanagpur Gneisses were emplaced at c. 1.65 Ga in an arc setting. The earliest accretion event at c. 1.56 Ga involved northward subduction and amalgamation of the Upper Bonai Group with the Singhbhum craton followed by accretion of the Gangpur Group with the Singhbhum craton–Upper Bonai Group composite at c. 1.45 Ga. Finally, continent–continent collision at c. 0.96 Ga led to the accretion of the CGC with the Singhbhum craton–Upper Bonai Group–Gangpur Group crustal units, synchronous with emplacement of pegmatitic granites. The geological events recorded in the GSB and other units of the CITZ only partially overlap with those in the Trans North China Orogen and the Capricorn Orogen of Western Australia, indicating that these suture zones are not correlatable. 相似文献
6.
The Purulia carbonatite of West Bengal, India is a dyke occurring within the 100 km long South Purulia Shear Zone (SPSZ), which marks the boundary between the Singhbhum Group of Rocks and the Chhotanagpur Granite Gneissic Complex (CGGC). It is composed essentially of calcite with apatite, amphibole, phlogopite, biotite, magnetite and ilmenite as common accessories. Based on optical properties and mineral chemistry two varieties of the amphibole are recognized: magnesiokatophorite and richterite. The latter is characterized by a relatively high content of Si and Na, while the former is enriched in Al and Ca. Such a composition of the amphibole is characteristic for the intermediate to the late stage carbonatite development. These two co-existing amphiboles reflect a sudden variation in total pressure within the magma chamber during the intrusion of the carbonatite dyke. It is inferred that the magnesiokatophorite started crystallizing first along with calcite and apatite. Subsequently, the ascent of carbonatitic magma to a more shallow depth (hypabyssal) resulted in the formation of the richterite. The difference in amphibole composition reflects a variation in the total pressure within the magma chamber that took place during the formation of the Purulia carbonatite. However, an alternative explanation, such as wallrock contamination, or liquid immiscibility, followed by carbonate magma segregation or magma mixing, may also be possible. There is, however, no evidence corroborating such an interpretation. 相似文献
7.
库车新生代构造性质和变形时间 总被引：126，自引：6，他引：120
库车构造位于南天山古生代碰撞造山带之南,为塔里木盆地最北的一个构造带。它自北而南可分为边缘逆冲（ 隐伏构造楔） 、斯的克背斜带、北部线性背斜带、拜城盆地、南部背斜带。每个背斜带又包含有若干逆冲断层相关褶皱,它们是断层转折褶皱、断层传播褶皱、滑脱褶皱、断层传播 滑脱混生褶皱、双重逆冲构造、突发构造、三角带构造。底部逆冲断层向南变浅,堆叠逆冲岩席向南变薄,总体上形成一个向南的逆冲构造楔。逆冲断层在斯的克背斜带侵位最早（２５ Ｍａ） ,在北部线性背斜带为１６９ Ｍａ,拜城盆地中的大宛其背斜为３６ Ｍａ,南部背斜带为５３ Ｍａ（ 北部） 和１８ Ｍａ（ 南部） ,变形作用向南变新。库车构造是印 藏板块碰撞的内陆构造响应,是二叠纪前陆盆地复活而成的再生前陆盆地变形带 相似文献
8.
Sahendra Singh Karun Kumar Chandan Vandana Jha 《Journal of the Geological Society of India》2018,92(2):166-172
The Mesoproterozoic metasedimentary units of Chandil Formation belong to the northern part of Singhbhum crustal province, eastern India. The Formation lies north of Dalma volcano-sedimentary belt and is separated from the Meso- Neoproterozoic Chhotanagpur granite gneissic complex (CGGC) by Tamar-Porapahar shear zone (TPSZ), i.e. South Purulia shear zone, (SPSZ) at its northern boundary. The metasedimentary unit comprises of quartz-mica-sericite-schist, quartzite, amphibolites and carbonaceous phyllites, which have not been studied well, so far in terms of their geochemistry, source rock and provenance characterization. In this work, the existing gaps in all those aspects are studied to infer the provenance of these metasedimentary sequences. The high silica contents of the Chandil Formation (~95% for the quartzites and ~70% for the metapelites) and low trace element concentrations indicate silica-rich source. The REE patterns of the quartzites and the metapelites exhibit LREE enrichment and HREE depletion with moderate negative Eu-anomalies which strongly favor felsic nature of the provenance. The significant enrichment of LREE, flat HREE patterns and negative Eu-anomalies of the metapelites suggest their derivation from an old upper continental crust, which is composed of felsic components and the negative Eu-anomalies indicate intra-crustal differentiation. The higher concentrations of the HFSE i.e. Zr, Hf and Ta, within the Chandil metasediments relative to those of EPC (Early Proterozoic Continental Crust), also suggests a felsic provenance. The geochemical signatures of the Chandil metasediments indicate that the sediments were derived during a prolonged period of weathering due to the slow upliftment and unroofing of the southern evolving Singhbhum granitic complex (SGC). 相似文献
9.
乌孙山北缘断裂位于新疆伊宁盆地南部,是伊宁盆地与乌孙山的边界断裂,由多条平行或斜列的次级断层组成.断裂呈近东西走向,总体倾向南,山前主断裂主要表现为高角度逆冲,倾角50°~80°,前缘冲断面相对较缓.断裂上盘主要由石炭系-二叠系组成,下盘主要为第四系和侏罗系,断层两盘沉积物的ESR年代表明断裂带多处错断中、上更新统地层.野外地层接触关系和区域构造研究表明,在中更新世末以来,断裂强烈向北逆冲,与伊犁盆地北缘断裂共同控制了盆山地貌格局.伊宁盆地及邻区中更新世末的区域构造运动与青藏高原的共和运动时代相当,这次事件由南北天山向伊犁盆地的对冲挤压引起,动力来源于青藏高原向外扩展生长. 相似文献
10.
基于多封闭系统低温热年代学特征的浅部地貌构造模型重建在揭示褶皱冲断带-前陆盆地系统形成演化过程中受到越来越广泛的重视与应用。青藏高原东缘龙门山地区多封闭系统低温年代学年龄总体上具有逐渐从冲断带前缘、由SE向NW至高原内部减小趋势,且走向上由NE向SW也具微弱减小趋势;龙门山褶皱冲断带热年代学年龄变化范围明显大于高原内部,揭示出盆-山过渡带新生代加强的褶皱冲断剥蚀浅表作用。基于龙门山区域低温热年代学和褶皱冲断带-前陆盆地系统稳态冲断剥蚀热模型,揭示出青藏高原东向扩展速率约为5～10 mm/a,抬升剥蚀速率为0.4～1.0 mm/a和龙门山褶皱冲断带缩短速率为0～15 mm/a,它们与现今地质学和大地测量学特征具有较好的一致性。因此,青藏高原东缘由西向东的多封闭系统热年代学年龄特征反映出新生代稳态的高原东向扩展生长过程,即龙门山褶皱冲断带冲断扩展和浅表剥蚀作用耦合过程。 相似文献
11.
CUI Junwen CHEN Wen LI Pengwu ZHANG Xiaowei LI Li Institute of Geology Chinese Academy of Geological Sciences Beijing 《《地质学报》英文版》2003,77(4):468-478
The western segment of the East Kunlun Mountains is one of the poorly studied regions in northwestern China. Through a structural analysis of the typical sections, we have the following views: (1) There is a very well developed fault system in the western segment of the East Kunlun Mountains and thrust propagation, normal slip and decoupling are the chief deformation events in this area. (2) Although the thrusting started in the Late Carboniferous and Late Triassic-Early Jurassic, strong activity took place in the Miocene-Quaternary when the Kumkol basin was strongly downwarped. (3) The tectonic pattern of coexistence of N-directed thrust propagation and S-directed normal slip in this area is consistent with the general tectonic pattern of the northern Qinghai-Tibet plateau and also very similar to that of the Himalayan region on the southern margin of the Qinghai-Tibet plateau, but their directions between the thrust propagation are opposite and all the strong thrust propagations occurred from the Mioc 相似文献
12.
ＮＥＥ向阿尔金主断裂带的新构造运动以左旋压扭性活动为特征，仅西端发育张性构造，并可划分出两期变形，新构造运动强度在时间上自上新世晚期开始至第四纪断裂活动强度增大，在空间上自ＳＷＷ向ＮＥＥ方向断裂活动强度逐渐减弱；柴达木北缘的新构造运动可划分为两期，其主要构造特征表现为向柴达木盆地逆冲的前进式叠瓦道冲带，柴达木盆地第四纪时的北界相对于第三纪时的北界向南迁移了数十公里；河西走廊盆地的新构造运动主要表现为盆地边缘断裂的逆冲兼走滑，盆地接受新生代沉积、盆地内第三系的轴面南倾的褶皱；ＮＥＥ向阿尔金主断裂带与其南侧的ＮＷＷ向断裂带是在统一构造应力场作用下相互协调、同时活动的两组关系紧密的构造带，两者的共同活动构成了断块运动。 相似文献
13.
塔西北柯坪剪切挤压构造 总被引：28，自引：3，他引：25
塔里木西北的柯坪地区存在着再变形的逆冲岩席。研究表明塔里木盆地西北边界断层－阿合奇断层为一巨型左行走滑断层。它在新生代的总走滑量达３０４ｋｍ,具有与塔里木盆地东南边界阿尔金断层相同量级的走滑量。阿合奇断层与阿尔金断层造成了阿合奇－西昆仑－西南塔里木－阿尔金断层剪切挤压构造系统。 相似文献
14.
South Purulia Shear Zone in India is an important zone that hosts uranium mineralization. Since detailed geophysical studies have not been carried out in this region, an integrated geophysical study using self-potential, resistivity, very low frequency electromagnetic and radiometric methods was performed to identify the subsurface structures that could host the hydrothermally altered uranium deposits in the area. The study reveals the wide and large magnitude of negative self-potential anomaly across the South Purulia Shear Zone. The peak negative self-potential anomalies are correlated with the low gravity and low resistivity anomalies measured along various profiles. The low self-potential, gravity and low resistivity anomaly zones are also correlated with conducting zones inferred from very low frequency electromagnetic measurements. Interpretation of self-potential data reveals multiple thick sheet-type vertical and/or inclined structures which might be associated with uranium mineralization. Schlumberger resistivity sounding data reveals an increasing trend of apparent resistivity with current electrode separations/depth. Apparent conductance measured simultaneously with resistivity measurement reveals an increase in current flow of current as depth increases. This exhibits the presence of thin conducting layers at these depths, which is not reflected in resistivity sounding data due to suppression problem. Also this conducting layer is consistent in various soundings and is connected from Raghunathpur to the South Purulia Shear Zone. Correlation of very low frequency and self-potential data shows that the structures are comparable and a radiometric profile also advocate that the conducting structure is associated with radioactive minerals. These structures are likely to be mineralized zones as hydro-uranium anomaly has also been reported from various locations in the area. Moreover, drilling results at a specific mine near the study area also confirms the presence of uranium mineralization. The hydrothermal activity associated with uranium mineralization seems to be still active in the area. Such combined geophysical studies are essential to understand this highly complex shear zone for the economic exploitation of its natural resources. 相似文献
15.
北秦岭二郎坪岩群南、北两侧分别被朱夏韧性剪切带和瓦乔韧性剪切带与秦岭岩群和宽坪岩群分开,这两条韧性剪切带对二郎坪弧后盆地的演化起着十分重要的作用。本文对这两条剪切带进行了详细的几何学、运动学和40Ar-39Ar年代学研究。几何学和运动学分析结果指示瓦乔剪切带具有由北向南逆冲剪切的运动学特征,而朱夏剪切带早期具有由南向北逆冲的运动学特征,而后期又发生右行走滑活动。对瓦乔剪切带和朱夏剪切带内的糜棱岩中白云母进行了40Ar-39Ar法定年,结果指示瓦乔剪切带逆冲活动发生在387±1.7 Ma,朱夏韧性剪切早期逆冲发生在晚古生代,后期右行走滑的年龄为146±2.8 Ma。综合两条剪切带的构造变形特征和年代学数据,结合前人的地质资料,本文认为二郎坪弧后盆地曾沿着瓦乔剪切带和朱夏剪切带发生双向式俯冲。 相似文献
16.
鄂尔多斯盆地侏罗纪西界分析 总被引：1，自引：0，他引：1
鄂尔多斯盆地西界,特别是其早—中侏罗世盆地西界,由于不同期次、不同性质的构造相互叠加而模糊不清,究竟是在贺兰山以西还是现在银川盆地以东的问题,至今尚无共识,极大地影响着矿产资源的评价和找矿战略的部署。本文在前人工作的基础上,通过针对性的野外工作,分析和筛分了不同时期的古构造,探讨了晚侏罗世和早—中侏罗世盆地的西界。文章认为,鄂尔多斯盆地西部巨大的近南北向挤压构造形成于晚侏罗世,而东西向的挤压构造则出现于晚三叠世。两期方向截然不同的挤压构造相互叠加,构成了鄂尔多斯盆地西部复杂的叠加构造和不规则的盆地西界。晚期挤压构造较为清晰,表现为近南北向的逆冲推覆构造带和纵贯盆地南北的"古脊梁",使盆地西界退缩到桌子山东麓断裂、横山堡—磁窑堡断褶带以及马儿庄冲断裂和崆峒山断裂以东。早期挤压构造受后期构造的叠加改造,断断续续,时隐时现。近东西向挤压构造受古亚洲域的影响,是印支运动的产物,近南北向挤压构造转受滨太平洋域的作用,是燕山运动的表现。在古亚洲域向太平洋域转换过程中的早—中侏罗世,鄂尔多斯盆地西部出现了近东西向的拉张伸展,在盆地内部表现为近东西向隆起凹陷的古地形,使盆地西缘波状弯曲,而非平直,"银川古隆起"和"汝箕沟—鄂... 相似文献
17.
《International Geology Review》2012,54(3):290-301
Structural investigations in the Precambrian Singhbhum Shear Zone of eastern India document an intimate relationship between micro- to meso-scale structures and the deformation history. Shear zone rocks are characterized by composite foliation, a well-developed stretching lineation, folds, shear planes, and quartz veins. These structures reflect thrusting of the Proterozoic north Singhbhum hanging wall block over the Archaean south Singhbhum footwall block. Microstructural analysis of multiple foliation and mylonitic rocks within the shear zone helps to define its progressive evolution. During progressive deformation, overprinting of microstructures resulted in incomplete transposition or complete erasing of previously formed structures and mineral assemblages, allowing room for new dynamic equilibrium structures to form. The dominant deformation mechanism was dissolution–recrystallization, with locally important fluid circulation responsible for transformation of the quartzo-feldspathic mass into phyllonite, and quartzites and schists into mylonite. Textural features suggest that the bulk deformation was non-coaxial, evolving from dominant pure shear in the early stage followed by simple shear in a single progressive strain history of the Singhbhum Shear Zone. 相似文献
18.
CENOZOIC FAULTING ALONG THE SOUTHEASTERN EDGE OF THE TIBETAN PLATEAU IN THE YANYUAN AREA AND ITS TECTONIC IMPLICATIONS 相似文献
19.
Structural analysis of the Chhotanagpur gneiss and the adjoining schistose rocks of the Singhbhum Group indicates perfect
conformity in their structures on macroscopic, mesoscopic and microscopic scales. This precludes the possibility of the gneissic
rocks having intruded into the deformed and metamorphozed schistose rocks. The observed features can be best explained by
considering the gneissic rocks as the basement and the schistose rocks as the cover, both deformed and metamorphozed together.
However, this does not exclude the possibility of the gneissic rocks being reactivated and intruding elsewhere. 相似文献
20.
《China Geology》2018,1(4):466-476
Based on the seismic data gathered in past years and the correlation between the sea and land areas of the Lower Yangtze Platform, the structural characteristics of the South Yellow Sea Basin since the Indosinian tectonic movement is studied in this paper. Three stages of structural deformation can be distinguished in the South Yellow Sea Basin since the Indosinian. The first stage, Late Indosinian to Early Yanshanian, was dominated by foreland deformation including both the uplifting and subsidence stages under an intensively compressional environment. The second stage, which is called the Huangqiao Event in the middle Yanshanian, was a change for stress fields from compression to extension. While in the third stage (the Sanduo Event) in the Late Himalayan, the basin developed a depression in the Neogene-Quaternary after rifting in the Late Cretaceous-Paleogene. The long-time evolution controlled 3 basin formation stages from a foreland basin, then a fault basin to a final depression basin. In conclusion, since the Indosinian, the South Yellow Sea Basin has experienced compressional fold and thrust, collisional orogen, compressional and tensional pulsation, strike-slip, extensional fault block and inversion structures, compression and convergence. The NE, NEE, nearly EW and NW trending structures developed in the basin. From west to east, the structural trend changed from NEE to near EW to NW. While from north to south, they changed from NEE to near EW with a strong-weak-strong zoning sequence. Vertically, the marine and terrestrial facies basins show a “seesaw” pattern with fold and thrust in the early stages, which is strong in the north and weak in the south and an extensional fault in later stages, which is strong in the north and weak in the south. In the marine facies basin, thrust deformation is more prevailing in the upper structural layer than that in the lower layer. The tectonic mechanism in the South Yellow Sea Basin is mainly affected by the collision between the Yangtze and North China Block, while the stress environment of large-scale strike-slip faults was owing to subduction of the Paleo-Pacific plate. The southern part of the Laoshan uplift is a weak deformation zone as well as a stress release zone, and the Meso-Paleozoic had been weakly reformed in later stages. The southern part of the Laoshan uplift is believed, therefore, to be a promising area for oil and gas exploration. 相似文献